Deflecting signal generator



Dec 20 i949 vA. c. MuNsTER ETAL ZAQLSM DEFLECTING SIGNAL GENERATOR Filed Nov. e; 194e Patented Dec. 20, 1949 Simstein; ('Jynwyd,l Pa., assignorsto Philco Corporation, Philadelphia, Pa.; a. corporation of4 Pennsylvania Application November 8, 1946, ,Serial No. 708,540

7 Claims.'

Tfiisi'nventioirrrelates to' sweep` signal `genera'-` tors for cathode ray tube and like circuits. More particularly it relates to methodsof and'rneans fr generating sweep signals' for" application to the deiiectingelements' of a? cathode ray tube" to deect thecatliodearay beam'A and to cause." it to describeea'z-spiral traceonth'e screenroirtheftubef Italsotrelateszto a: particular; form -of sweep sig-- nalfor application to fthe deflectingelements of. a'fcathoden'aytube tofproduce'such avtrace;

'Ilher inventiom is: particularly applicable in Y a` radarrmoving; target indicators'systein of, these.- called storaeetype: Ing-such a .systemnitissrequiretofstorefor preservaior moreor lessiex.. tctrdedzperiods-of time,V information contained in an electrical .wave signal whichvaries asia func-4 tion of time throughout intervalssof.,appreciable duration.vv Such .periods of Y storage may, Yin generalQ... be. comparable in duration.. to the intervals duringwhich .the informationrtofbe .preserved occurs: The dllrations oi these intervals may correspond.,to.the pulserepetition period of Vtheradar system, which,` for. a typical system, may be of the orden of500 microseconds.

A convenient methodjof achieving such storage is'y to provide a cathode raytube whose electron beam iscausedg bythe application'of locally genera-ted deectingsignalspto scan a suitably retentivescieen' orjmosaic vin a predetermined 'systematicmanner.' vThe signaltobe stored'is then caused to modulate`A either the; deflection or the intensity ofthe-electron beam; whereby the intel-- ligence-containediin the signal is transferredto the screen in the frm'pf a persistent` trace; a

characteristic` ofv which varies throughout* its e length in the l samev way that? the corresponding cliaracteristictof the; signal L varied ast a. function of time. Atssom'e laterftimeftheztracethus formed mayfagain besseanned (e. gf. by -anelectron orlight beam) Y tof reconstruct` a f, sig-nalv corresponding: to theone J which was ,used toA produce the trace. i

Alternatively, in `one..type fof moving Atarget indicator hereinafterreferredto as thestorage and subtractivetype, Yit .may be desirable ,to compare thestoreel` signalwith a subsequent radar signal which' differs Afromtl'ie firstsignalowing` to the motion; oftarget'sf' in the interim,V andi tov derive irectly asignalindi'cative of-v'diierences between the two signals:- To this end*thetwo.signalsfare causedi successively tm deflectionfmodulate.- the normal '1 scans produced .z by locally generated 'deecting signals Itisknownithat diierenccs in thetracesthus produced :will fea-use chargestoV be induced im af capacitor platedocated fadjacentfthe screernorrychch thetrace isproduced. Thuszthere 2 may "be derived signals indicative of differences between the earlier-and later-signals produced by target motion.

Because the'informatonl to be' storedmayiex tendover a relatively long interval 'of\time; and'in' orderto preserve the information-asaccurately as possible; it is desirabletoprovide,` in avsingle cathode ray tube used' for" storagef purposes; as long a trace aspossible: However; to.avoid::am^. biguity and'fconfusion', it is-essential thatzthe trace bet notv permitted' to." intersect" itselfduring.; any storagexperiod and' that ay predeterminedmela tively uniform spacingbe .maintained betweendiff-V ferentzportionsof the sametrace-,which areiproxi mate oneto the other; A- furtherfrequirement isf that there should.' bea-no1 sharp Ydiscontini-iities inthe traceproduced. A trace which satisfies these :requirements Aand which ypermits maximum utilization of the-available screen'areaisionelof spiral form.

Moreover, ina systemof-the storageiand ,subtractive typeabove referred to, `successivetraces are usually initiated. in response to. the.` pulses which Vcontrol the transmission oi` radar pulses of high frequency y energy,A The spacing., of, these controlling. pulses will generally vary. somewhat.' anditls essential, despite this variation, thatsub'- sequently produced traces shouldcoincide almost identically with those previously produced; To this end it is necessaryto produce;-atarbitrarily` different times, deecting signals which are-sube stantially identical inform and amplitude:

'In the past, deiiecting signals for producing a spiral trace of gradually diminishing amplitude have been generated'by successivelyapplying` ima pulses of current to a pair ofiparallelftunedcir-f cuits to produce'dampedsine-wavev-signals. B5; appropriately timing lthe application'A ofthe-impulses; these signals could be maintainediin'mor'e-i or'lessphase quadrature relationshiplsuitable for application to the horizontal 'and-'vertical deect ing plates respectively of Fa conventionalelectro' staticallyedeflected cathode fray 'tube to:E produce the desired spiral trace; Howevenib'ecause ofthe inherent resistance offthe means usedfto apply an impulse of: current toa".parallelitunedicrcuim some nite` time is requiredjto. charge: thev cons denser: thereof:A As: a'zresult,iktl 1er electron-beam; which is initially at rest atfthecenter of the tube, requiresl a nitetime tobe deflectedto ltheexterfnal periphery of .the Itube screen, at-which .point itisdesired to commence-the storagetracel. This makesY it` diiicult tov synchronize; the inceptionof thesweep With1the occurrence of.. a,pulse. which controls the opera-tion 0L thev` radar, transmitter.

Furthermore, if, as above suggested, the same parallel resonant circuit is to be successively shockexcited in response to control pulses which tend to occur aperiodically, the conditions existing in the resonant circuit upon successive excitations will differ. This will give rise to undesirable variations in the phases and amplitudes of the deflecting signals generated.

In accordance with the invention, the cathode ray beam is normally deflected away from the central axis of the tube. At the desired instant, suitable deecting forces are applied to produce a spiral-conical scan of diminishing amplitude. Deecting signals adapted to produce these results, when applied to the deilecting plates of a conventional electrostatically-defiected cathode ray tube, may be derived from a circuit comprising inductance, capacitance and resistance in series. Means are provided which normally maintain a predetermined amount of energy stored in the reactive elements of the circuit. Further means are provided which are actuatable to permit this stored energy to iiow in oscillatory manner in the series circuit. Owing to the presence of resistance these oscillations are damped. From the circuit there may then be derived defiecting potential waves proportional respectively to the potential across the capacitance and'to the current in the series circuit. These waves will be of damped sinusoidal form and will be in substantial phase quadrature depending upon the magnitude of the resistance in the series circuit. At Ythe termination of the sweep, the interchange of energy between the reactive elements is inhibited and preferably they are returned to their previous condition of energy storage so that the circuit will be in condition, when again actuated, to generate identical deflecting signals. Y Accordingly it is the primary object of the invention to provide means for deiiecting the electron beam of a cathode ray tube to produce, on the screen thereof, a spiral trace of diminishing amplitude commencing at a predetermined time at a desired point on said screen.

Another object is to provide means for producing successive spiral traces which are substantially identical in form, despite the fact that the intervals separating the initiation of successive traces may vary in duration.

Still another object is to provide a deflecting wave of particular form adapted to produce the desired trace as above dened.

Other features and advantages of the invention will become apparent from a consideration o f the following specication with reference to the accompanying drawings in which Figures 1, 2 and 3 illustrate waveforms to which reference will be made in explaining the principle of the invention and the mode of operation of a representative embodiment as shown in the schematic diagram of Figure 4.

' VIn Figure 1 the solid line represents the damped cosine waveform obtained by the customary expedient of applying a current impulse to a parallel tuned circuit at the time t1. As already mentioned, because of the inherent resistance of the means used to do this, the wave does not attain its maximum positive value until a finite time later. The broken line modication represents the deilecting signal required to produce a trace commencing at time t1 at a point on the external periphery of the tube, but which is unobtainable practically by this method. Likewise, as aforementioned, the amplitude and phase of successive deflecting waves generated by this expedient will vary depending on the energy remaining in the circuit at the time of its activation by a given impulse.

In Figure 2 is represented one of the two defiecting signals developed in accordance with the method of the invention by the circuit of Figure 4. It will be noted that, during the interval from t1 to t2 and commencing at a point I corresponding to maximum deiiection, this signal alternates with gradually diminishing amplitude on either side of the zero-deflection level represented by broken line 2. Prior to t1 the signal is at a level corresponding to maximum deflection. Thus it will be seen to be such as will cause the beam of the cathode ray tube, to which it is applied, to be deected to a point on the external periphery of the tube screen at time t1.

Similarly, in Figure 3, there is represented the counterpart of the deecting signal shown in Figure 2. During the interval ifi-t2, and commencing at the zero-deection level represented by broken line 3, this Ysignal alternates with gradually diminishing amplitude on either side of line 3 and lags the signal of Figure 2 by approximately in phase. By reason of the fact that it is derived from the same series resonant lcircuit as the signal of Figure 2, it will, prior to t1, have a value corresponding to maximum deflection. However, at time t1, this value is substantially instantaneously reduced to initiate the trace at the desired point on the cathode ray tube screen.

Referring now to Figure 4. the circuit for producing these deflecting signals cornnrisea'basically, triode tubes ai, 5, 6 and 1, condenser t and inductor 9. The tubes are connected to form a circuit whose operation is similar in many respects to the conventional Eccles-Jordan or nip-nop circuit. Tubes 4 and 5 are normally conductive and are connected in series with resistors I0, II and I2 between a point of positive potential and ground. Condenser 8 is connected from the cathode of tube Ii to ground. Resistors I 0, II and I2 and tubes 4 and 5, while thev are conducting, form an eiective voltage divider which operates to maintain a positive charge on condenser. 8. Tubes 5 and 'I are normally nonconductive and are connected in series with resistors I3, I4 and I2 between a source of positive potential and ground. With tubes and 'i cut off, no current flows through inductor S connecting the cathodes of tubes 4 and B.

Upon the application of a negative triggering pulse I5 of suiiicient amplitude through condenser IE to the grid of tube 5, the latter will cease to conduct and, by reason of the resultant reduction of the current in resistory I2, common to the cathode circuits of both tubes 5 and l, the potential of the cathode of tube 'I will be lowered suiciently to cause it tocommence conducting. Current will commence to flow through inductor 9, resistor I4, tube 'F and resistor 52. Through the action of inductor 9 in impeding such flow, the potentials of the plate of tube i and the cathode of tube S will be made instantaneously more negative. By virtue of connection I1 from the plate of tube 'I to the grid of blib@ 4, the latter will be cut ofi, Also tube l, by

ter of the screen, to proceed during. some finite time to the external periphery of the screen folllowing a trace of the sort represented at 35 in Figure 4. Moreover, as is apparent, suitable de fleeting signals for this purpose may be derived from a single Ytuned circuit, whereby diiculties arising owing to discrepancies in the tuning of two separate circuits are avoided.A

For illustrative purposes only, and with no thought of imposing any limitation'upon the invention, the following typical values are given for the components of the circuit of Figure 4:

It will of course be understood that the invention is susceptible of embodiment in physical forms other than the one here shown, such as will occur to those skilled in the art upon reading this specication. Accordingly, the scope of the invention is to be regarded as subject only to the limitations imposed by the appendedclaims.

l. In a signal generator, inductive and capacitive reactive means, a source of energy, normally conductive vacuum tube means arranged conN trollably to supply energy from said source to said capacitive reactive means and operative normally to maintain a predetermined amount of said energy stored in said reactive means, a connection between said inductive and capacitive reactive means, normally non-conductive vacuum tube means for inhibiting the Vflow of current in said inductive means, means responsive to a triggering impulse for causing said normally conductive means to cease conducting and for causing said normally non-conductive means to conduct and permit interchange of energy between said reactive means, means for restoring said vacuum tube means to their normal conductive and non-'con'- ductive conditions to terminate said energy interchange and to restore said reactive means to their normal condition of energy storage, and means for deriving a signal which is a function oi said energy interchange.

2. In a signal generator, serially connected inductive and capacitative reactive means, a source of energy, normally conductive vacuum tube means arranged controllably to supply energy from said source to said capacitive reactive means and operative normally to maintain a predetermined amount of said energy stored in said reactive means,normally non-conductive vacuum tube means for inhibiting the flow of current in said inductive means, means responsive tov a triggering impulse for causing said normally conductive means to cease conducting and for causing said normally non-conductive means to conduct and permit interchange of energy between said reactive means, means for restoring said vacuum tube means to their normal conductive and non-con- Vductive conditions tov terminate Said energy inter- Vchange and to restore said reactive means to' their normal condition of energy storage, and means including said vacuum tube fmeans for deriving 8 an amplified signal which is a function of said energy interchange. Y

3. Inra signal generator, a circuit comprising inductive and capacitive reactive elements, means normally operative to apply a potential to said capacitive element for maintaining a predetermined amount of energy stored therein, said means being actuatable to discontinue the application of said potential to said element, a connection between said inductive and capacitive reactive elements providing for the interchange of energy between said elements, means normally inhibiting'the ow of current in said inductive element, said last-named means being actuatable to permit the flow of current in said inductive element, means for simultaneously actuating said potential applying means and said current inhibiting means to discontinue the application of said potential to said capacitive element and to permit the free oscillatory interchange of energy between said reactive elements, means for subsequently discontinuing the actuation of said potential applying means and said current inhibiting means to inhibit said oscillatory energy interchange and to Vrestore said capacitive element to its normal condition of energy storage, and means for deriving from said circuit a signal which is a function of said energy interchange.

4. In a signal generator, a circuit comprising inductive and capacitive reactive elements, normally conductive vacuum tube means, said means being operative, when conductive, to apply a potential to said capacitive element for maintaining a predetermined amount of energy stored in said capacitive element and, when rendered non-conductive, to discontinue the application of said potential to said element, a connection between said inductive and capacitive reactive elements providing for the interchange of energy between said elements, normally non-conductive vacuum tube means, said last-named means being operative, when non-conductive, to inhibit the flow of current in said inductive element and, when rendered conductive, to permit flow of current in said inductive element, means for rendering said first named vacuum tube means non-conductive and for rendering said last-named vacuum tube means simultaneously conductive to permit free oscillatory interchange of energy between said reactive elements While said first and lastenamed vacuum tube means are respectively non-conduc tive and conductive, and means for returning said two vacuum tube means to their normal conductive and non-conductive conditions respectively, whereby ypromptly to inhibit said oscillatory energy interchange and to restore said capacitive element to its normal condition of energy storage.

5. A signal generator according to claim 3 including means operative a predetermined time after the actuation of said potential-applying and current-inhibiting means to restore said means to their normal conditions.

- 6. .In a signal generator according to claim 4, a condenser, means responsive to the rendering nonconductive of said normally conductive vacuum tube means for initiating a progressive al- Iteration in charge on said condenser, and means responsive to the alteration in potential across said condenser resulting from said alteration in charge for restoring said normally conductive and said normally non-conductive vacuum tube means to their normal conditions a predetermined time after the rendering nonconductive of said normally conductive vacuum tube means.

7. In a cathode ray system, a cathode ray tube, said tube comprising a screen, means for producing an electron beam directed along an axis which intercepts said screen, and a pair of substantially orthogonal beam deecting elements, means initially biasing each of said deflecting elements with equal potentials to produce substantially equal deflection of said beam in mutually perpendicular directions away from said axis, the biasing of each of said elements being insufcient in itself to deect said beam off said screen, but the biasing of both of said elements being sueient cooperatively to deect said beam off said screen, and means actuatable to apply to said deflecting ele ments damped sinusoidally Varying deectlng signals in substantial phase-quadrature relationship commencing at the time of actuation of said means, the maximum amplitude of each of said deecting signals being such as to produce deflections substantially equal to the deections produced by said initial biasing, application oi said deection signals causing said beam to trace 10 upon said screen a substantially spiral path commencing at a point near the boundary of said screen substantially immediately following the actuation of said means.

ALLEN C. MNSTER. DAVID E. SUNSTEIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,181,309 Andrieu Nov. 28, 1939 2,300,999 Williams Nov. 3, 1942 2,307,237 Rea et a1 Jan. 5, 1943 2,408,414 Donaldson Oct. 1, 1946 FOREIGN PATENTS Number Country Date 406,903 Great Britain Mar. 8, 1934 

